Many combustion systems mix fuel and air prior to the fuel air mixture being provided to the combustion chamber. Many of these premixed combustion systems use a venturi device to regulate the air fuel ratio. The basic principle is that air for combustion is pulled (or pushed) through a venturi-shaped pathway. The venturi pathway reduces the cross-sectional area at the venturi throat which causes an increase of flow velocity thus reducing pressure. It is this low pressure which induces fuel flow from a fuel source which is at a higher pressure than the low pressure found at the venturi throat into the air stream from a separate port. This pneumatic coupling is useful since these combustion systems can maintain an air fuel ratio even when the airflow changes whether intentionally or accidentally.
Reducing the airflow from its maximum and through its minimum, and vice versa, is often done with a variable speed blower. This adjustment allows the system to operate at different input rates. The ratio between the maximum flow and the minimum flow is referred to as a turndown ratio. These systems often only work within a certain operating range because as the venturi throat becomes oversized at lower flow rates and does not increase the velocity enough to lower pressure sufficiently to properly induce required fuel flow.
Accordingly, it is desirable to provide a system and method which allows an apparatus to operate with broader operating parameters. In other words, a system and method may operate along a broader turndown ratio.